1988 Volume 6 Issue 4 Pages 486-492
A new pressure joining method has been developed for transition joints between aluminum and copper pipes. The joining procedure is characterized by the following steps. 1) The ends of aluminum and copper pipes are set into contact with each other under a initial pressure that does net result in plastic deformation of the pipes. 2) The pipes are rapidly heated by an induction mtehod up to a temperature just above the eutectic temperature. 3) After an adequate quantity of eutetic liquid is formed, a second pressure, which is highre than the initial pressure, is applied to exclude the eutectic liquid out of the interface. Changes in the length of aluminum and copper pipe are detected to estimate the quantity of eutectic liquid. When the length changes by a predetermined value, the heating is terminated to cool the joint and the second pressure is applied.
Many pipes of diameter 8 mm were joined in a protective gas atmosphere under various condition for the amount of eutectic liquid and the second pressure. The joints were evaluated by a metallographic examination, mechanical tests and leak tests. The residual eutectic layer at the joining interface becomes thinner with increasing second pressure. Joints with a layer less than 0.1 μm in thickness were obtained at a pressure of 30 MPa. Joints with such thin layers never break down at the joining interface during repeated bending fracture tests, but the aluminum pipes break down outside the interface. The leak rate of helium in the joints with thin residual eutectic layers is less than 1×10-13Pa m3/s even after joints were subjected to repeated bendings, thermal cycles and flattening deformations.